It wouldn't cost too much to upgrade it. I actually just got done rebuilding the Official Highlander Board here: http://www.highlander-community.com so I have some idea what's entailed. Maybe $400 in all for the upgrade, the installation, and the skin customization. If there's interest we can look at doing a little GoFundMe or such.

Take a look at that link and you'll see what a 5.3.2 vBulletin board looks like. It's mobile friendly out of the box and has "Likes" and Facebook integration. This board has been stuck at 3.8.3 for a while now, and is no longer supported.